Gallium nitride type semiconductor laser device

ABSTRACT

A gallium nitride type semiconductor laser device includes: a substrate; and a layered structure formed on the substrate. The layered structure at least includes an active layer of a nitride type semiconductor material which is interposed between a pair of nitride type semiconductor layers each functioning as a cladding layer or a guide layer. A current is injected into a stripe region in the layered structure having a width smaller than a width of the active layer. The width of the stripe region is in a range between about 0.2 μm and about 1.8 μm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gallium nitride type semiconductorlaser device for use in a light source of an optical disk system.

2. Description of the Related Art

A gallium nitride type semiconductor (e.g., GaInAlN) is used as asemiconductor material for a semiconductor laser device (LD) having anemission wavelength in a wavelength range from ultraviolet to green. Forexample, MRS Internet J. Nitride Semicond. Res., vol. 2, no. 5 (1997)describes a semiconductor laser device using such a gallium nitride typesemiconductor, as illustrated in a cross-sectional view in FIG. 11.

Referring to FIG. 11, the semiconductor laser device has, on a sapphiresubstrate 201, a GaN buffer layer 202, an n-GaN contact layer 203, ann-In_(0.05)Ga_(0.95)N layer 204, an n-Al_(0.08)Ga_(0.92)N cladding layer205, an n-GaN guide layer 206, a multiquantum well structure activelayer 207 including In_(0.15)Ga_(0.85)N quantum well layers andIn_(0.02)Ga_(0.98)N barrier layers, a p-Al_(0.2)Ga_(0.8)N layer 208, ap-GaN guide layer 209, a p-Al_(0.08)Ga_(0.92)N cladding layer 210, ap-GaN contact layer 211, a p-side electrode 212 and an n-side electrode213. The multiquantum well structure active layer 207 includes sevenlayers in total, i.e., four In_(0.15)Ga_(0.85)N quantum well layers eachhaving a thickness of about 3.5 nm and three In_(0.02)Ga_(0.98)N barrierlayers each having a thickness of about 7 nm. In the multi-quantum wellstructure active layer 207, the quantum well layers and the barrierlayers alternate with each other.

In this conventional example, the p-Al_(0.08)Ga_(0.92)N cladding layer210 and the p-GaN contact layer 211 are formed in a ridge stripe patternso as to constrict an injected current. The width of the stripe patternis about 4 μm.

Japanese Laid-open Publication No. p9-232680 describes a semiconductorlaser device similarly using a gallium nitride type semiconductor, whichalso includes a ridge stripe structure having a stripe width of about 5μm to about 10 μm for constricting an injected current.

When employing a semiconductor laser device using a gallium nitride typesemiconductor as a light source of an optical disk system, in order toprevent a read error from occurring due to noise during a data readoperation, a self-pulsation type semiconductor laser is employed inwhich an optical output is modulated for a constant current injected.Such a semiconductor laser device is described in Japanese Laid-openPublication No. 9-191160, for example.

FIG. 12 is a cross-sectional view illustrating such a semiconductorlaser device. Referring to FIG. 12, the semiconductor laser deviceincludes an n-SiC substrate 221, an n-AlN buffer layer 222, ann-Al_(0.15)Ga_(0.85)N cladding layer 223, an In_(0.15)Ga_(0.85)N activelayer 224 having a thickness of about 50 nm, a p-Al_(0.15)Ga_(0.85)Nfirst p-type cladding layer 225, a p-In_(0.2)Ga_(0.8)N saturableabsorbing layer 226, an n-Al_(0.25)Ga_(0.75)N current blocking layer227, a p-Al_(0.15)Ga_(0.85)N second p-type cladding layer 228, a p-GaNcap layer 229, a p-GaN contact layer 230, a p-side electrode 231 and ann-side electrode 232.

In this conventional example, a portion of light generated by the activelayer 224 is absorbed by the saturable absorbing layer 226, therebycausing an absorption coefficient of the saturable absorbing layer 226to change. Accordingly, an intensity of light emission by a laseroscillation from the active layer 224 is changed periodically. As aresult, coherence of the emitted light from the laser is reduced. Thisconventional example also includes a ridge stripe structure having astripe width of about 2 μm for constricting an injected current.

When employing such a semiconductor laser device with reduced coherenceas a light source of an optical disk system, even if light reflected bythe disk returns to the semiconductor laser, the emitted light from thelaser does not interfere with the reflected return light, therebysuppressing generation of noise and thus preventing a data read errorfrom occurring.

However, the conventional laser device using a gallium nitride typesemiconductor has the following problems.

First, in the self-pulsation type semiconductor laser device having thesaturable absorbing layer, light generated by the active layer isabsorbed by the saturable absorbing layer, thereby increasing the lossof light within the laser cavity. As a result, the oscillation thresholdcurrent of the semiconductor laser device increases, and the emissionefficiency is reduced. Moreover, in this conventional self-pulsationtype semiconductor laser device, since the saturable absorbing layer isadded only to one of the cladding layers interposing the active layertherebetween or only to one of the guide layers interposing the activelayer therebetween, the far field pattern of the emitted light from thelaser is asymmetric, whereby the focused spot size cannot be madesufficiently small when focusing the emitted light with a lens.

The conventional laser device using a gallium nitride type semiconductorto which the saturable absorbing layer is not added does not have suchproblems (e.g., the increased oscillation threshold current, the reducedemission efficiency, and incapability to have a small focused spot size)as those seen in the conventional self-pulsation type semiconductorlaser device. However, when this semiconductor laser device is used as alight source of an optical disk system, noise occurs due to the returnlight from the disk, thereby causing a read error during a data readoperation. Therefore, the conventional laser device using a galliumnitride type semiconductor to which the saturable absorbing layer is notadded is not suitable for a light source of an optical disk system.

SUMMARY OF THE INVENTION

A gallium nitride type semiconductor laser device of the presentinvention includes: a substrate; and a layered structure formed on thesubstrate. The layered structure at least includes an active layer of anitride type semiconductor material which is interposed between a pairof nitride type semiconductor layers each functioning as a claddinglayer or a guide layer. A current is injected into a stripe region inthe layered structure having a width smaller than a width of the activelayer. The width of the stripe region is in a range between about 0.2 μmand about 1.8 μm.

Preferably, a portion of the active layer existing outside the striperegion has a width of at least about 3 μm.

The active layer may include a single quantum well layer.

Alternatively, the active layer may include a multiquantum wellstructure including a plurality of quantum well layers and at least onebarrier layer each interposed between the adjacent two quantum welllayers, the number of the quantum well layers being two, three or four.

A thickness of each quantum well layer in the active layer may be about10 nm or less.

A thickness of each of the at least one barrier layer in the activelayer may be about 10 nm or less.

In one embodiment, the layered structure at least includes a firstcladding layer having a first conductivity type, the active layer, asecond cladding layer having a second conductivity type, and a contactlayer having the second conductivity type, which are deposited in thisorder. The second cladding layer and the contact layer are formed in astripe having a width smaller than the width of the active layer. Andthe layered structure further includes a current blocking layerdeposited outside the stripe.

In another embodiment, the layered structure at least includes a firstcladding layer having a first conductivity type, the active layer, aguide layer or a second cladding layer having a second conductivitytype, and a current blocking layer. A striped groove is provided in thecurrent blocking layer so as to reach the guide layer or the secondcladding layer having the second conductivity type, the groove having awidth smaller than the width of the active layer. And the layeredstructure further includes at least another cladding layer having thesecond conductivity type and a contact layer having the secondconductivity type which are deposited in this order in the stripedgroove and on the current blocking layer.

In still another embodiment, the layered structure at least includes acontact layer or a cladding layer having a first conductivity type, anda current blocking layer, which are deposited in this order. A stripegroove is provided in the current blocking layer so as to reach thecontact layer or the cladding layer having the first conductivity type.And the layered structure further includes at least another claddinglayer having the first conductivity type, the active layer, a claddinglayer having a second conductivity type, and a contact layer having thesecond conductivity type, which are deposited in this order in thestriped groove and on the current blocking layer.

The current blocking layer may include a dielectric insulation film.

The current blocking layer may be made of a semiconductor materialhaving an energy gap which is equal to or smaller than an energy gap ofthe active layer.

The current blocking layer may be made of a semiconductor materialhaving a refractive index which is less than or equal to a refractiveindex of the cladding layer having the second conductivity.

For example, the current blocking layer may be made of a nitride typesemiconductor material.

A thickness of a gallium nitride type semiconductor layer included inthe layered structure and interposed between a portion of the activelayer outside the stripe region and the current blocking layer may be ina range between about 0.01 μm and about 0.8 μm.

Thus, the invention described herein makes possible the advantage ofproviding a gallium nitride type semiconductor laser device which solvesthe above-described problems associated with the conventional galliumnitride type semiconductor laser devices, and which is thereforesuitably used as a light source of an optical disk system withsatisfactory laser oscillation characteristics.

This and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a semiconductor laserdevice according to Example 1 of the present invention;

FIG. 2 is a cross-sectional view illustrating a semiconductor laserdevice according to Example 2 of the present invention;

FIG. 3 is a cross-sectional view illustrating a semiconductor laserdevice according to Example 5 of the present invention;

FIG. 4 is a cross-sectional view illustrating a semiconductor laserdevice according to Example 6 of the present invention;

FIG. 5 is a cross-sectional view illustrating a semiconductor laserdevice according to Example 7 of the present invention;

FIG. 6 is a cross-sectional view illustrating a semiconductor laserdevice according to Example 8 of the present invention;

FIG. 7 is a cross-sectional view illustrating a semiconductor laserdevice according to Example 9 of the present invention;

FIG. 8 is a cross-sectional view illustrating a semiconductor laserdevice of the present invention in which a width of a current injectionstripe region is less than that of a conventional device;

FIG. 9 is a graph illustrating how an oscillation threshold currentvalue changes as a width of a current injection stripe region is varied;

FIG. 10 is a graph illustrating how an oscillation threshold currentvalue changes as a thickness of a gallium nitride type semiconductorlayer interposed between a portion of an active layer outside a currentinjection stripe region and a current blocking layer is varied;

FIG. 11 is a cross-sectional view illustrating a conventionalsemiconductor laser device using a gallium nitride type semiconductor;and

FIG. 12 is a cross-sectional view illustrating a conventionalsemiconductor laser device of a self-pulsation type using a galliumnitride type semiconductor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to achieve the present invention, the inventor has conductedintensive study to find solutions for the above-described problemsassociated with the conventional devices, and found that aself-pulsation type semiconductor laser device can be realized in asimple structure without a saturable absorbing layer which is used inthe conventional self-pulsation type semiconductor laser devices.

A gallium nitride type semiconductor laser device according to thepresent invention has an active layer of a nitride semiconductorinterposed between cladding layer and/or guide layers of a nitridesemiconductor. The semiconductor laser device includes a “currentinjection stripe region” (a stripe region into which a current isinjected) having a width less than the width of the active layer. Thewidth of the stripe region is in a range between about 0.2 μm to about1.8 μm.

FIG. 8 is a cross-sectional view illustrating a semiconductor laserdevice in which the width of the current injection stripe region is lessthan that of the conventional gallium nitride type semiconductor laserdevice. In this case, since the stripe region is narrow, the lateralmode of the laser light is wider than the width of the current injectionstripe region. Then, the laser light existing in a region outside thestripe region can be absorbed by a portion of the active layer whichexists in the region. Therefore, the portion of the active layer whichexists outside the current injection stripe region functions as asaturable absorbing layer, thereby providing self-pulsationcharacteristics.

When the width of the current injection stripe region is large as in theconventional gallium nitride type semiconductor laser device, the areaoutside the stripe region where the laser light exists is small, therebyresulting in only a reduced saturable absorbing function thereof.Therefore, the self-pulsation characteristic is not obtained.

According to the present invention, there is a slight increase in theoscillation threshold current density because the laser light isabsorbed in a portion of the active layer outside the current injectionstripe region. However, the oscillation threshold current value itselfis not increased since the width of the current injection stripe regionis reduced, thereby obtaining a gallium nitride type semiconductor laserdevice having satisfactory laser oscillation characteristics.

FIG. 9 is a graph illustrating how the oscillation threshold currentvalue changes as the width of the current injection stripe region isvaried. FIG. 9 shows that the self-pulsation characteristic is notobtained for a width of the stripe region of about 2 μm or greater wherethe width of the current injection stripe region is increased, and theoscillation threshold current value is also increased. Moreover, whenthe width of the current injection stripe region is less than about 0.2μm, the oscillation threshold current density is substantiallyincreased, thereby increasing the oscillation threshold current valueitself. Thus, it is possible to obtain a gallium nitride typesemiconductor laser device exhibiting self-pulsation characteristicswith a low oscillation threshold current value and satisfactory laseroscillation characteristics by designing the width of the currentinjection stripe region to be in a range between about 0.2 μm and about1.8 μm.

Thus, for the portion of the active layer outside the current injectionstripe region to function as a saturable absorbing layer, the portionpreferably has a width of at least about 3 μm. When the width of theportion is less than about 3 μm, there is only a reduced saturableabsorbing effect, and the self-pulsation is not obtained.

When the width of the current injection stripe region is reduced as inthe present invention, and a material such as a gallium arsenide typesemiconductor material (AlGaAs) or an indium phosphide typesemiconductor material (InGaAsP) is used, the threshold current mayincrease because of a current being injected into a region larger thanthe width of the stripe. However, it has been found that when a galliumnitride type semiconductor is used, there is little current spreadingsince the electric resistance value is large. Thus, the thresholdcurrent is small, and the lateral mode of the laser light is stable atthe width of the current injection region.

Moreover, when a gallium nitride type semiconductor layer is used, thecurrent spreading is little even when the stripe width is reduced, it ispossible to have a relatively thick gallium nitride type semiconductorlayer between the portion of the active layer outside the currentinjection stripe region and a current blocking layer. Therefore, it isnot necessary to precisely control the thickness of that gallium nitridetype semiconductor layer, thereby improving the production yield.

However, if the thickness of the gallium nitride type semiconductorlayer interposed between the portion of the active layer outside thecurrent injection stripe region and the current blocking layer isexcessively large, the current spreading out of the stripe region isincreased even when using a gallium nitride type semiconductor materialhaving a large electric resistance, whereby the self-pulsationcharacteristic is not obtained.

FIG. 10 is a graph illustrating how the oscillation threshold currentvalue changes as the thickness of the gallium nitride type semiconductorlayer interposed between the portion of the active layer outside thecurrent injection stripe region and the current blocking layer is variedin the structure of Example 1 which will be described in detail later.FIG. 10 illustrates two cases where the width of the current injectionstripe region is about 1.5 μm and about 0.5 μm, respectively.

In either case, the current spreading occurs and the oscillationthreshold current value increases when the thickness of the galliumnitride type semiconductor layer (specifically, referring to the totalthickness of a p-GaN guide layer 8 and a p-Al_(0.1)Ga_(0.9)N p-typecladding layer 9, see Example 1) is greater than about 0.8 μm. Moreover,when the thickness of the gallium nitride type semiconductor layer isless than about 0.01 μm, the current blocking layer does not functionproperly, thereby increasing the amount of a leak current and theoscillation threshold current value. Furthermore, it has been confirmedthat self-pulsation occurs when the thickness of the gallium nitridetype semiconductor layer interposed between the active layer and thecurrent blocking layer is in a range between about 0.01 μm and about 0.8μm.

Thus, when the thickness of the gallium nitride type semiconductor layeris reduced to be about 0.8 μm or less, the current spreading issuppressed, and there is obtained a gallium nitride type semiconductorlaser device having a stable self-pulsation characteristic. Furthermore,when the thickness of the gallium nitride type semiconductor layer isabout 0.01 μm or greater, the active layer and the current blockinglayer are spatially separated from each other and are allowed to haverespective functions thereof separately, whereby there is obtained agallium nitride type semiconductor laser device having self-pulsationcharacteristics.

While FIG. 10 illustrates an example where GaN is used for the guidelayers and Al_(0.1)Ga_(0.9)N is used for the cladding layers, variousdevices have been actually produced with guide layers of Al_(x)Ga_(1−x)N(0≦x≦0.2) and cladding layers of Al_(y)Ga_(1−y)N (0≦y≦0.3), where x≦y(e.g., x=y=0.1; x=0, y=0.3; or x=0.05, Y=0.2). Any of the variousdevices produced exhibit characteristics substantially the same as thoseillustrated in FIG. 10. Thus, as long as the compositions of thematerials used are within the above ranges, it is possible to reduce theoscillation threshold current value and to provide low noisecharacteristics resulting from self-pulsation by designing the thicknessof the gallium nitride type semiconductor layer interposed between theactive layer and the current blocking layer to be in a range betweenabout 0.01 μm and about 0.8 μm. It has also been confirmed that a lowoscillation threshold value current can be realized within substantiallythe same thickness range even when indium (In) is added to the guidelayers or the cladding layers in an amount of about 10% or less as thecomposition of the III group atom.

In order to obtain the self-pulsation type semiconductor laser device ofthe present invention, densities of electrons and holes existing in theactive layer should be rapidly modulated. However, mobilities ofelectrons or holes of the gallium nitride type semiconductor materialused for the active layer are significantly low because of largeeffective mass of electrons/holes and a large number of crystal defectsexisting therein. Therefore, even when electrons and holes disappearthrough emission recombination, new electrons or holes are not injectedby diffusion, whereby densities of electrons and holes are less likelyto be modulated.

In view of this, in the present invention, the active layer of thegallium nitride type semiconductor laser device is formed in a singlequantum well layer or a multiquantum well structure (including quantumwell layers and barrier layers formed in an alternate pattern, where thenumber of the quantum well layers is in a range between 2 and 4), withthe thickness of each quantum well layer in the active layer being about10 nm or less. In this way, electrons and holes are more easilydiffused, and densities of electrons and holes are more easilymodulated. As a result, there is obtained a gallium nitride typesemiconductor laser device having a stable self-pulsationcharacteristic.

Moreover, in the case where the active layer employs the multiquantumwell structure, if the barrier layer in the active layer is excessivelythick, uniform distributions of electrons and holes across the activelayer are inhibited. Therefore, the electrons and holes are less likelyto be re-combined, thereby deteriorating the self-pulsationcharacteristics. However, by designing the thickness of the barrierlayer to be about 10 nm or less, the holes and electrons are distributeduniformly in the active layer, thereby obtaining a gallium nitride typesemiconductor laser device having satisfactory self-pulsationcharacteristics.

Unlike a semiconductor laser device using a material such as a galliumarsenide type semiconductor material (AlGaAs) or an indium phosphidetype semiconductor material (InGaAsP), the gallium nitride typesemiconductor laser device includes a large number of defects in thecurrent injection stripe region. However, according to the presentinvention, the number of defects present in the region is reduced byreducing the width of the stripe region, thereby preventingdeterioration of the laser characteristics and improving the reliabilityof the device.

The present invention will now be described in greater detail withreference to illustrative examples.

EXAMPLE 1

FIG. 1 is a cross-sectional view illustrating a gallium nitride typesemiconductor laser device according to Example 1 of the presentinvention.

Referring to FIG. 1, the gallium nitride type semiconductor laser deviceincludes a sapphire substrate 1 having a c-plane as a top surfacethereof, a GaN buffer layer 2, an n-GaN n-type contact layer 3, ann-Al_(0.1)Ga_(0.9)N n-type cladding layer 4, an n-GaN guide layer 5, amultiquantum well structure active layer 6 including twoIn_(0.2)Ga_(0.8)N quantum well layers and a single In_(0.05)Ga_(0.95)Nbarrier layer, an Al_(0.2)Ga_(0.8)N evaporation prevention layer 7, ap-GaN guide layer 8, a p-Al_(0.1)Ga_(0.9)N p-type cladding layer 9, ap-GaN p-type contact layer 10, a p-side electrode 11, an n-sideelectrode 12 and a SiO₂ insulation film 13.

In the present invention, the sapphire substrate 1 may alternativelyhave any other orientation such as an a-plane, an r-plane or an m-plane.Moreover, a GaN substrate, a SiC substrate, a spinel substrate, a MgOsubstrate, a Si substrate, a GaAs substrate, or the like, may be usedinstead of a sapphire substrate. Particularly, a GaN substrate and a SiCsubstrate are advantageous in that they have a lattice constant which iscloser to that of a gallium nitride type semiconductor materialdeposited thereon, as compared with a sapphire substrate, therebyresulting in a film with good crystallinity. Furthermore, they arerelatively easily cleaved, thereby facilitating formation of a lasercavity end face by cleavage.

The buffer layer 2 need not be made of GaN but may alternatively be madeof any other material, e.g., AlN or AlGaN ternary mixed crystal as longas a gallium nitride type semiconductor material can be epitaxiallygrown thereon.

Each of the n-type cladding layer 4 and the p-type cladding layer 9 mayalternatively be made of an AlGaN ternary mixed crystal having an Alcomposition other than Al_(0.1)Ga_(0.9)N. When the Al composition isincreased, the energy gap difference and the refractive index differencebetween the active layer and the cladding layers increases, therebyeffectively confining carriers and light within the active layer. Thisallows for reduction of the oscillation threshold current andimprovement of the temperature characteristic. Decreasing the Alcomposition to such an extent that the confinement of carriers and lightis maintained increases the mobility of the carriers in the claddinglayers, thereby allowing for reduction of the device resistance of thesemiconductor laser device. Moreover, each of these cladding layers mayalternatively be made of a quaternary mixed crystal semiconductor, or amixed crystal semiconductor of more than four elements which furthercontains one or more additional elements in a small amount.

It should be noted that the n-type cladding layer 4 and the p-typecladding layer 9 need not have the same mixed crystal composition.

Each of the guide layers 5 and 8 need not be made of GaN but mayalternatively be made of any other material, e.g., an InGaN or AlGaNternary mixed crystal, an InGaAlN quaternary mixed crystal, or the like,as long as the material has an energy gap value between that of thequantum well layer forming the multiquantum well structure active layer6 and that of the cladding layers 4 and 9. Moreover, a donor or anacceptor need not be doped entirely across the guide layers.Alternatively, a portion of the guide layers closer to the multiquantumwell structure active layer 6 may be non-doped, or the entire guidelayers may be non-doped. In such a case, fewer carriers exist in theguide layers, thereby reducing the amount of light absorbed by freecarriers and allowing for further reduction of the oscillation thresholdcurrent. Furthermore, the guide layer may be optional in some cases, anda gallium nitride type semiconductor laser device without guide layersmay still function as a semiconductor laser device.

The respective compositions of the two In_(0.2)Ga_(0.8)N quantum welllayers and the single In_(0.05)Ga_(0.95)N barrier layer of themultiquantum well structure active layer 6 may be set to be suitable forthe desired laser oscillation wavelength. For example, when a longeroscillation wavelength is desired, the In composition of the quantumwell layer may be increased, and when a shorter oscillation wavelengthis desired, the In composition of the quantum well layer may bedecreased. Furthermore, each of the quantum well layer and the barrierlayer may be made of a quaternary mixed crystal semiconductor, or amixed crystal semiconductor of more than four elements which furthercontains one or more additional elements in a small amount in additionto the InGaN ternary mixed crystal. The barrier layers may be simplymade of GaN.

In the present example, the Al_(0.2)Ga_(0.8)N evaporation preventionlayer 7 is formed in contact with the multiquantum well structure activelayer 6 in order to prevent evaporation of the quantum well layer whilethe growth temperature is increased. Therefore, any other material orstructure may be used as the evaporation prevention layer 7 as long asit protects the quantum well layer. For example, an AlGaN ternary mixedcrystal having a different Al composition or GaN may be used. Moreover,Mg may be doped into the evaporation prevention layer 7. In such a case,the injection of holes through the p-GaN guide layer 8 or thep-Al_(0.1)Ga_(0.9)N p-type cladding layer 9 can be facilitated.

Furthermore, when the In composition of the quantum well layer isrelatively small, the quantum well layer is not substantially evaporatedeven if the evaporation prevention layer 7 is not provided. Thus, evenif the evaporation prevention layer 7 is not provided in such a case,the characteristics of the gallium nitride type semiconductor laserdevice according to the present example will not be lost ordeteriorated.

Referring to FIG. 1, a method for producing the above-described galliumnitride type semiconductor laser device will now be described. In thefollowing, an MOCVD method (a metal organic chemical vapor depositionmethod) is employed. However, any other vapor phase growth method withwhich GaN can be epitaxially grown may alternatively be used, e.g., anMBE method (molecular beam epitaxial growth method) or an HVPE method (ahydride vapor phase epitaxial growth method).

First, the GaN buffer layer 2 is grown to be about 35 nm in thickness ata growth temperature of about 550° C., using trimethylgallium (TMG) andammonium (NH₃) as source materials, on the sapphire substrate 1 having ac-plane as a top surface thereof which has been positioned in apreselected growth oven.

Then, the growth temperature is increased to about 1050° C., and theSi-doped n-GaN n-type contact layer 3 is grown to be about 3 μm inthickness, using TMG, NH₃ and a silane gas (SiH₄) as source materials.Then, trimethylaluminum (TMA) is added to the source materials, and theSi-doped n-Al_(0.1)Ga_(0.9)N n-type cladding layer 4 is grown to beabout 0.7 pm in thickness while maintaining the growth temperature atabout 1050° C. Then, TMA is removed from the source materials, and theSi-doped n-GaN guide layer 5 is grown to be about 0.05 μm in thicknesswhile maintaining the growth temperature at about 1050° C.

Next, the growth temperature is reduced to about 750° C., and anIn_(0.2)Ga_(0.8)N quantum-well layer (thickness: about 5 nm), anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm) and anotherIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm) are grownin this order, using TMG, NH₃ and trimethylindium (TMI) as sourcematerials, thereby providing the multiquantum well structure activelayer 6 (total thickness: about 15 nm). Then, the Al_(0.2)Ga_(0.8)Nevaporation prevention layer 7 is grown to be about 10 nm in thickness,using TMG, TMA and NH₃ as source materials, while maintaining the growthtemperature at about 750° C.

Next, the growth temperature is increased again to about 1050° C., andthe Mg-doped p-GaN guide layer 8 is grown to be about 0.05 μm inthickness, using TMG, NH₃ and cyclopentadienylmagnesium (Cp₂Mg) assource materials. Then, TMA is added to the source materials, and theMg-doped p-Al_(0.1)Ga_(0.9)N p-type cladding layer 9 is grown to beabout 0.7 μm in thickness while maintaining the growth temperature atabout 1050° C. Then, TMA is removed from the source materials, and theMg-doped p-GaN p-type contact layer 10 is grown to be about 0.2 μm inthickness while maintaining the growth temperature at about 1050° C.Thus, a gallium nitride type epitaxial wafer is produced.

Then, the wafer is annealed in a nitrogen gas atmosphere at about 800°C., so as to reduce the resistance of the Mg-doped p-type layers.

Thereafter, using ordinary photolithography and dry etching techniques,an etching process is performed to remove portions of the p-GaN p-typecontact layer 10 and the other layers thereunder in a stripe pattern sothat the n-GaN n-type contact layer 3 is exposed therethrough, therebyforming a mesa structure having a width of about 200 μm. Next, using thesimilar photolithography and dry etching techniques, another etchingprocess is performed to remove portions of the remaining p-GaN p-typecontact layer 10 and the p-Al_(0.1)Ga_(0.9)N p-type cladding layer 9 soas to form a ridge structure having a width of about 1.5 μm. The stripedridge structure is preferably separated by about 3 μm or more from eachside of the mesa structure having a width of about 200 μm. In thepresent example, the striped ridge structure is provided so as to beseparated by about 10 μm from a side of the mesa structure on which then-side electrode 12 is formed. When the striped ridge structure is thusprovided close to the n-side electrode 12 as in this example, theelectric resistance and thus the operating voltage is reduced.

During the dry etching process, the etching is stopped before reachingthe multiquantum well structure active layer 6 so as to suppress damageto the active layer due to the etching, thereby preventing thereliability of the device from decreasing and the oscillation thresholdcurrent value from increasing. In addition, in the present example, theportion of the p-Al_(0.1)Ga_(0.1)N p-type cladding layer 9 remainingunetched outside the stripe region has a thickness of about 0.3 μm.This, even in combination with the p-GaN guide layer 8, is thinner thanabout 0.8 μm, thereby suppressing the current spreading.

Then, a SiO₂ insulation film 13 having a thickness of about 200 nm isformed as a current blocking layer on the side surfaces of the ridge andthe surface of the p-type layer, except for a portion of the surfacewhere the ridge is provided. The p-side electrode 11 of nickel and goldis formed on the surface of the SiO₂ insulation film 13 and the p-GaNp-type contact layer 10. The n-side electrode 12 of titanium andaluminum is formed on the surface of the n-GaN n-type contact layer 3which has been exposed by the etching process. Thus, a gallium nitridetype LD wafer is produced.

Then, the wafer is cleaved along a direction perpendicular to thedirection of the ridge stripe so as to provide laser cavity end faces.Each of the cleaved wafer pieces is further divided into individualchips. Each chip is mounted on a stem, and the electrodes arerespectively connected to lead terminals by wire bonding, therebyproducing a gallium nitride type semiconductor laser device.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 20 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation. When the gallium nitride typesemiconductor laser device of this example is used in an optical disksystem, a data read error is prevented.

Thus, there is provided a gallium nitride type semiconductor laserdevice which can be put into practical use.

In the present example, the width of the current injection stripe regionis about 1.5 μm. However, substantially the same effect can be achievedwith any other width of the stripe region in a range between about 0.2μm and about 1.8 μm.

In the present example, each of the quantum well layers and the barrierlayer of the multiquantum well structure active layer 6 has a thicknessof about 5 nm. However, these layers need not have the same thicknessbut may alternatively have different thicknesses. Moreover,substantially the same effect can be achieved as long as each of theselayers has a thickness of about 10 nm or less. Furthermore, themultiquantum well structure active layer 6 may alternatively includethree or four quantum well layers, or it may alternatively be a singlequantum well layer structure active layer.

In the present example, the laser cavity end faces are provided bycleavage. However, a sapphire substrate may sometimes be so hard that itis difficult to be cleaved. In such a case, the laser cavity end facesmay alternatively be provided by a dry etching process.

Moreover, since a sapphire substrate, which is an insulator, is used inthe present example, the n-side electrode 12 is formed on the surface ofthe n-GaN n-type contact layer 3 which has been exposed by the etchingprocess. Alternatively, when GaN, SiC, Si, GaAs, or the like, having then-type conductivity, is used for the substrate, the n-side electrode 12may be formed on the reverse side of the substrate. In such a case, theetching process for producing a striped mesa structure having a width ofabout 200 μm may be optional, and the striped ridge structure into whicha current is injected may be separated by about 3 μm or more from eachend of the semiconductor laser device chip.

Moreover, the p-type and n-type conductivities may be reversed in theabove explanation.

EXAMPLE 2

FIG. 2 is a cross-sectional view illustrating a gallium nitride typesemiconductor laser device according to Example 2 of the presentinvention.

Referring to FIG. 2, the gallium nitride type semiconductor laser deviceincludes a sapphire substrate 21 having a c-plane as a top surfacethereof, a GaN buffer layer 22, an n-GaN n-type contact layer 23, ann-Al_(0.1)Ga_(0.9)N n-type cladding layer 24, an n-GaN guide layer 25, amultiquantum well structure active layer 26 including twoIn_(0.2)Ga_(0.8)N quantum well layers and three In_(0.05)Ga_(0.95)Nbarrier layers, a p-GaN guide layer 27, a p-In_(0.05)Ga_(0.95)N etchingstopping layer 28, a p-Al_(0.1)Ga_(0.9)N p-type cladding layer 29, ap-GaN p-type contact layer 30, a p-side electrode 31, an n-sideelectrode 32 and a SiO₂ insulation film 33.

In the present example, since the In_(0.05)Ga_(0.95)N barrier layerwhich has a low In composition is provided as the top layer of themultiquantum well structure active layer 26, the Al_(0.2)Ga_(0.8)Nevaporation prevention layer is not deposited. Moreover, thep-In_(0.05)Ga_(0.95)N etching stopping layer 28 is deposited on thep-GaN guide layer 27. Other than the above, the gallium nitride typesemiconductor laser device is produced in substantially the same manneras in Example 1.

Referring to FIG. 2, a method for producing the gallium nitride typesemiconductor laser device of the present example will now be described.In the following, an MOCVD method is employed. However, any other vaporphase growth method with which GaN can be epitaxially grown mayalternatively be used, e.g., an MBE method or an HVPE method.

First, the GaN buffer layer 22 is grown to be about 35 nm in thicknessat a growth temperature of about 550° C., using TMG and NH₃ as sourcematerials, on the sapphire substrate 1 having a c-plane as a top surfacethereof which has been positioned in a preselected growth oven.

Then, the growth temperature is increased to about 1050° C., and theSi-doped n-GaN n-type contact layer 23 is grown to be about 3 μm inthickness, using TMG, NH₃ and a SiH₄ as source materials. Then, TMA isadded to the source materials, and the Si-doped n-Al_(0.1)Ga_(0.9)Nn-type cladding layer 24 is grown to be about 0.7 μm in thickness whilemaintaining the growth temperature at about 1050° C. Then, TMA isremoved from the source materials, and the Si-doped n-GaN guide layer 25is grown to be about 0.05 μm in thickness while maintaining the growthtemperature at about 1050° C.

Next, the growth temperature is reduced to about 750° C., and anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm) anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm), anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm) and anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm) are grown inthis order, using TMG, NH₃ and TMI as source materials, therebyproviding the multiquantum well structure active layer 26 (totalthickness: about 25 nm).

Next, the growth temperature is increased again to about 1050° C., andthe Mg-doped p-GaN guide layer 27 is grown to be about 0.05 μm inthickness, using TMG, NH₃ and Cp₂Mg as source materials. Then, thegrowth temperature is reduced to about 750° C., and thep-In_(0.05)Ga_(0.95)N etching stopping layer 28 is grown to be about0.02 μm in thickness, using TMG, NH₃, Cp₂Mg and TMI as source materials.

Then, the growth temperature is increased again to about 1050° C., andthe Mg-doped p-Al_(0.1)Ga_(0.9)N p-type cladding layer 29 is grown to beabout 0.7 μm in thickness, using TMG, NH₃, Cp₂Mg and TMA as sourcematerials. Then, TMA is removed from the source materials, and theMg-doped p-GaN p-type contact layer 30 is grown to be about 0.2 μm inthickness while maintaining the growth temperature at about 1050° C.Thus, a gallium nitride type epitaxial wafer is produced.

Then, the wafer is annealed in a nitrogen gas atmosphere at about 800°C., so as to reduce the resistance of the Mg-doped p-type layers.

Thereafter, using ordinary photolithography and dry etching techniques,an etching process is performed to remove portions of the p-GaN p-typecontact layer 30 and the other layers thereunder in a stripe pattern sothat the n-GaN n-type contact layer 23 is exposed, thereby forming amesa structure having a width of about 200 μm. Next, using the similarphotolithography and dry etching techniques, another etching process isperformed to remove portions of the remaining p-GaN p-type contact layer30 and the p-Al_(0.1)Ga_(0.9)N p-type cladding layer 29 so as to form aridge structure having a width of about 1.5 μm. In this process, Inatoms appear on the exposed surface when the etching reaches thep-In_(0.05)Ga_(0.95)N etching stopping layer 28. Thus, the etchingprocess can be stopped upon detection of the In atoms by elementanalysis, thereby precisely controlling the etching depth. The stripedridge structure is provided so as to be separated by about 10 μm from aside of the mesa structure on which the n-side electrode 32 is formed.

Then, a SiO₂ insulation film 33 having a thickness of about 200 nm isformed as a current blocking layer on the side surfaces of the ridge andthe surface of the p-type layer, except for a portion of the surfacewhere the ridge is provided. The p-side electrode 31 of nickel and goldis formed on the surface of the SiO₂ insulation film 33 and the p-GaNp-type contact layer 30. The n-side electrode 32 of titanium andaluminum is formed on the surface of the n-GaN n-type contact layer 23which has been exposed by the etching process. Thus, a gallium nitridetype LD wafer is produced.

Then, the wafer is cleaved along a direction perpendicular to thedirection of the ridge stripe so as to provide laser cavity end faces,and each of the cleaved wafer pieces is further divided into individualchips. Each chip is mounted on a stem, and the electrodes arerespectively connected to lead terminals by wire bonding, therebyproducing a gallium nitride type semiconductor laser device.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 20 mA, as in Example 1. Moreover,deterioration is not observed in these characteristics, and it isconfirmed that the device effects self-pulsation. When the galliumnitride type semiconductor laser device of this example is used in anoptical disk system, a data read error is prevented.

Thus, there is provided a gallium nitride type semiconductor laserdevice which can be put into practical use. Moreover, the use of theetching stopping layer improves the controllability of the etchingdepth, thereby reducing device characteristic variation among differentproduction lots.

In the present example, the width of the current injection stripe regionis about 1.5 μm. However, substantially the same effect can be achievedwith any other width of the stripe region in a range between about 0.2μm and about 1.8 μm.

In the present example, each of the quantum well layers and the barrierlayers of the multiquantum well structure active layer 26 has athickness of about 5 nm. However, these layers need not have the samethickness but may alternatively have different thicknesses. Moreover,substantially the same effect can be achieved as long as each of theselayers has a thickness of about 10 nm or less. Furthermore, themultiquantum well structure active layer 26 may alternatively includethree or four quantum well layers, or it may alternatively be a singlequantum well layer structure active layer.

In the present example, the laser cavity end faces are provided bycleavage. However, a sapphire substrate may sometimes be so hard that itis difficult to be cleaved. In such a case, the laser cavity end facesmay alternatively be provided by a dry etching process.

Moreover, since a sapphire substrate, which is an insulator, is used inthe present example, the n-side electrode 32 is formed on the surface ofthe n-GaN n-type contact layer 23 which has been exposed by the etchingprocess. Alternatively, when GaN, SiC, Si, GaAs, or the like, having then-type conductivity, is used for the substrate, the n-side electrode 32may be formed on the reverse side of the substrate. In such a case, theetching process for producing a striped mesa structure having a width ofabout 200 μm is optional, and the striped ridge structure into which acurrent is injected may be separated by about 3 μm or more from each endof the semiconductor laser device chip.

Moreover, the p-type and n-type conductivities may be reversed in theabove explanation.

In the present example, the p-In_(0.05)Ga_(0.95)N etching stopping layer28 is deposited on the p-GaN guide layer 27. Alternatively, thep-In_(0.05)Ga_(0.95)N etching stopping layer 28 may be provided in thep-GaN guide layer 27 or in the p-Al_(0.1)Ga_(0.9)N p-type cladding layer29. Moreover, the In composition of the p-In_(0.05)Ga_(0.95)N etchingstopping layer 28 is not limited to that described in the presentexample. Any other semiconductor material may alternatively be used aslong as it allows for determination of the etching depth.

EXAMPLE 3

A gallium nitride type semiconductor laser device according to Example 3of the present example is produced in substantially the same manner asthat in Example 2 except that a Si-doped n-In_(0.25)Ga_(0.75)N layerhaving a thickness of about 0.5 μm is provided as a current blockinglayer on the side surfaces of the striped ridge structure into which acurrent is injected and the surface of the p-type layer, except for aportion of the surface where the ridge is provided.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 20 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation.

In the present example, since light generated by the active layer isabsorbed by the Si-doped n-In_(0.25)Ga_(0.75)N current blocking layerprovided outside the current injection stripe region, the spreading ofthe lateral mode of the laser light is stabilized due to the lightabsorption by the current blocking layer, thereby allowing laser lightof a single lateral mode to be obtained with good reproducibility.

Moreover, the current blocking layer has the n-type conductivity in thepresent example. Holes as minority carriers generated by the lightabsorption in the current blocking layer have a short diffusion lengthand disappear quickly, and therefore will not flow through the currentblocking layer into the p-type cladding layer. Therefore, when alight-absorbing semiconductor material is used as a current blockinglayer, it preferably has n-type conductivity.

In the present example, the Si-doped n-In_(0.25)Ga_(0.75)N layer (about2.9 eV) is used as a current blocking layer. Alternatively, any othersemiconductor may be used as long as it has an energy gap less than orequal to that of the active layer (about 3.1 eV). For example, an InGaNternary mixed crystal nitride semiconductor having a different Incomposition, an AlGaInN quaternary mixed crystal nitride semiconductor,or a semiconductor other than a nitride semiconductor such as a galliumarsenide type semiconductor, an indium phosphide type semiconductor, aII-VI group semiconductor, a IV group semiconductor, or the like, may beused. However, when a gallium nitride type semiconductor is used for acurrent blocking layer, the thermal expansion coefficient, the latticeconstant and the crystalline structure thereof are similar to those ofthe other gallium nitride type semiconductors used for the active layeror the cladding layer. Thus, a current blocking layer having a goodcrystallinity can be formed, thereby improving the reliability of thelaser device.

EXAMPLE 4

A gallium nitride type semiconductor laser device according to Example 4of the present example is produced in substantially the same manner asthat in Example 2 except that a Si-doped n-Al_(0.25)Ga_(0.75)N layerhaving a thickness of about 0.5 μm is provided as a current blockinglayer on the side surfaces of each of the striped ridge structures intowhich a current is injected and the surface of the p-type layer, exceptfor a portion of the surface where the ridge is provided.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 18 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation.

In the present example, the refractive index (about 2.43) of theSi-doped n-Al_(0.25)Ga_(0.75)N current blocking layer provided outsidethe current injection stripe region is smaller than the refractive index(about 2.49) of the Mg-doped p-Al_(0.1)Ga_(0.9)N p-type cladding layer.Therefore, the effective refractive index inside the stripe region islarger than that outside the stripe region, so that the spreading of thelateral mode of the laser light is stabilized due to the refractiveindex difference. This allows laser light of a single lateral mode to beobtained with good reproducibility. Further-more, the Si-dopedn-Al_(0.25)Ga_(0.75)N current blocking layer does not absorb lightgenerated by the active layer, thereby allowing for further reduction ofthe oscillation threshold current value.

In the present example, the Si-doped n-Al_(0.25)Ga_(0.75)N layer is usedas a current blocking layer. Alternatively, any other semiconductor maybe used as long as it has a refractive index less than or equal to thatof the Mg-doped p-Al_(0.1)Ga_(0.9)N p-type cladding layer. For example,an AlGaN ternary mixed crystal nitride semiconductor having a differentAl composition, an AlGaInN quaternary mixed crystal nitridesemiconductor, or a semiconductor other than a nitride semiconductor maybe used. However, when a gallium nitride type semiconductor is used fora current blocking layer, the thermal expansion coefficient, the latticeconstant and the crystalline structure thereof are similar to those ofthe other gallium nitride type semiconductors used for the active layeror the cladding layer. Thus, a current blocking layer having a goodcrystallinity can be formed, thereby improving the reliability of thelaser device.

EXAMPLE 5

FIG. 3 is a cross-sectional view illustrating a gallium nitride typesemiconductor laser device according to Example 5 of the presentinvention.

Referring to FIG. 3, the gallium nitride type semiconductor laser deviceincludes a sapphire substrate 41 having a c face as a surface thereof, aGaN buffer layer 42, an n-GaN n-type contact layer 43, ann-Al_(0.1)Ga_(0.9)N n-type cladding layer 44, an n-GaN guide layer 45, amultiquantum well structure active layer 46 including threeIn_(0.2)Ga_(0.8)N quantum well layers and two In_(0.05)Ga_(0.95)Nbarrier layers, an Al_(0.2)Ga_(0.8)N evaporation prevention layer 47, ap-GaN guide layer 48, a p-Al_(0.1)Ga_(0.9)N p-type cladding layer 49, ap-GaN p-type contact layer 50, a p-side electrode 51, an n-sideelectrode 52 and a SiO₂ insulation film 53.

In the present invention, the sapphire substrate 41 may alternativelyhave any other orientation such as an a-plane, an r-plane or an m-plane.Moreover, a GaN substrate, a SiC substrate, a spinel substrate, a MgOsubstrate, a Si substrate, a GaAs substrate, or the like, may be usedinstead of a sapphire substrate. Particularly, a GaN substrate and a SiCsubstrate are advantageous in that they have a lattice constant which iscloser to that of a gallium nitride type semiconductor materialdeposited thereon, as compared to a sapphire substrate, therebyresulting in a film with good crystallinity. Furthermore, they arerelatively easily cleaved, thereby facilitating formation of a lasercavity end face by cleavage.

The buffer layer 42 need not be made of GaN but may alternatively bemade of any other material, e.g., AlN or AlGaN ternary mixed crystal aslong as a gallium nitride type semiconductor material can be epitaxiallygrown thereon.

Each of the n-type cladding layer 44 and the p-type cladding layer 49may alternatively be made of an AlGaN ternary mixed crystal having an Alcomposition other than Al_(0.1)Ga_(0.9)N. When the Al composition isincreased, the energy gap difference and the refractive index differencebetween the active layer and the cladding layers increases, therebyeffectively confining carriers and light within the active layer. Thisallows for reduction of the oscillation threshold current andimprovement of the temperature characteristic. Decreasing the Alcomposition to such an extent that the confinement of carriers and lightis maintained increases the mobility of the carriers in the claddinglayers, thereby allowing for reduction of the device resistance of thesemiconductor laser device. Moreover, each of these cladding layers mayalternatively be made of a quaternary mixed crystal semiconductor, or amixed crystal semiconductor of more than four elements which furthercontains one or more additional elements in a small amount.

It should be noted that the n-type cladding layer 44 and the p-typecladding layer 49 need not have the same mixed crystal composition.

Each of the guide layers 45 and 48 need not be made of GaN but mayalternatively be made of any other material, e.g., an InGaN or AlGaNternary mixed crystal, an InGaAlN quaternary mixed crystal, or the like,as long as the material has an energy gap value between that of thequantum well layer forming the multiquantum well structure active layer46 and that of the cladding layers 44 and 49. Moreover, a donor or anacceptor need not be doped entirely across the guide layers.Alternatively, a portion of the guide layers closer to the multiquantumwell structure active layer 46 may be non-doped, or the entire guidelayers may be non-doped. In such a case, fewer carriers exist in theguide layers, thereby reducing the amount of light absorbed by freecarriers and allowing for further reduction of the oscillation thresholdcurrent.

The respective compositions of the three In_(0.2)Ga_(0.8)N quantum welllayers and the two In_(0.05)Ga_(0.95)N barrier layers of themultiquantum well structure active layer 46 may be set to be suitablefor the desired laser oscillation wavelength. For example, when a longeroscillation wavelength is desired, the In composition of the quantumwell layer may be increased, and when a shorter oscillation wavelengthis desired, the In composition of the quantum well layer may bedecreased. Furthermore, each of the quantum well layer and the barrierlayer may be made of a quaternary mixed crystal semiconductor, or amixed crystal semiconductor of more than four elements which furthercontains one or more additional elements in a small amount in additionto the InGaN ternary mixed crystal. The barrier layers may be simplymade of GaN.

In the present example, the Al_(0.2)Ga_(0.8)N evaporation preventionlayer 47 is formed in contact with the multiquantum well structureactive layer 46 in order to prevent evaporation of the quantum welllayer while the growth temperature is increased. Therefore, any othermaterial or structure may be used as the evaporation prevention layer 47as long as it protects the quantum well layer. For example, an AlGaNternary mixed crystal having a different Al composition or GaN may beused. Moreover, Mg may be doped into the evaporation prevention layer47. In such a case, the injection of holes through the p-GaN guide layer48 or the p-Al_(0.1)Ga_(0.9)N p-type cladding layer 49 can befacilitated.

Furthermore, when the In composition of the quantum well layer isrelatively small, the quantum well layer is not substantially evaporatedeven if the evaporation prevention layer 47 is not provided. Thus, evenif the evaporation prevention layer 47 is not provided in such a case,the characteristics of the gallium nitride type semiconductor laserdevice according to the present example will not be lost ordeteriorated.

Referring to FIG. 3, a method for producing the above-described galliumnitride type semiconductor laser device will now be described. In thefollowing, an MOCVD method is employed. However, any other vapor phasegrowth method with which GaN can be epitaxially grown may alternativelybe used, e.g., an MBE method or an HVPE method.

First, the GaN buffer layer 42 is grown to be about 35 nm in thicknessat a growth temperature of about 550° C., using TMG and NH₃ as sourcematerials, on the sapphire substrate 41 having a c-plane as a topsurface thereof which has been positioned in a preselected growth oven.

Then, the growth temperature is increased to about 1050° C., and theSi-doped n-GaN n-type contact layer 43 is grown to be about 3 μm inthickness, using TMG, NH₃ and SiH₄ as source materials. Then, TMA isadded to the source materials, and the Si-doped n-Al_(0.1)Ga_(0.9)Nn-type cladding layer 44 is grown to be about 0.7 μm in thickness whilemaintaining the growth temperature at about 1050° C. Then, TMA isremoved from the source materials, and the Si-doped n-GaN guide layer 45is grown to be about 0.05 μm in thickness while maintaining the growthtemperature at about 1050° C.

Next, the growth temperature is reduced to about 750° C., and anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm), anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm) anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm) and anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm) are grownin this order, using TMG, NH₃ and TMI as source materials, therebyproviding the multiquantum well structure active layer 46 (totalthickness: about 25 nm). Then, the Al_(0.2)Ga_(0.8)N evaporationprevention layer 47 is grown to be about 10 nm in thickness, using TMG,TMA and NH₃ as source materials, while maintaining the growthtemperature at about 750° C. Next, the growth temperature is increasedagain to about 1050° C., and the Mg-doped p-GaN guide layer 48 is grownto be about 0.05 μm in thickness, using TMG, NH₃ and Cp₂Mg as sourcematerials.

After the above-described crystal growth steps, the resulting wafer istaken out of the growth oven, and the SiO₂ insulation film 53 having athickness of about 200 nm is formed as a current blocking layer on thesurface of the Mg-doped p-GaN guide layer 48. Thereafter, using ordinaryphotolithography and wet etching techniques, the SiO₂ insulation film 53is wet-etched with fluorine so as to form a striped groove having awidth of about 1.0 μm.

Then, the wafer is again positioned in the growth oven, and the Mg-dopedp-Al_(0.1)Ga_(0.9)N p-type cladding layer 49 is grown to be about 0.7 μmin thickness with a growth temperature of about 1050° C., using TMG,TMA, NH₃ and Cp₂Mg as source materials. Then, TMA is removed from thesource materials, and the Mg-doped p-GaN p-type contact layer 50 isgrown to be about 0.2 μm in thickness while maintaining the growthtemperature at about 1050° C. Thus, a gallium nitride type epitaxialwafer is produced. The p-Al_(0.1)Ga_(0.9)N p-type cladding layer 49 andthe p-GaN p-type contact layer 50 are formed in a ridge structurecentered along the striped groove having a width of about 1.0 μm.

Then, the wafer is annealed in a nitrogen gas atmosphere at about 800°C., so as to reduce the resistance of the Mg-doped p-type layers.

Thereafter, using ordinary photolithography and dry etching techniques,an etching process is performed to remove portions of the SiO₂insulation film 53 and the other layers thereunder where thep-Al_(0.1)Ga_(0.9)N p-type cladding layer 49 and the p-GaN p-typecontact layer 50 are not provided so that the n-GaN n-type contact layer43 is exposed. Thus, a striped mesa structure is provided having a widthof about 200 μm and including the ridge structure of thep-Al_(0.1)Ga_(0.9)N p-type cladding layer 49 and the p-GaN p-typecontact layer 50. The striped ridge structure of the p-Al_(0.1)Ga_(0.9)Np-type cladding layer 49 and the p-GaN p-type contact layer 50 ispreferably separated by about 3 μm or more from each side of the mesastructure having a width of about 200 μm. In the present example, thestriped ridge structure is provided so as to be separated by about 5 μmfrom a side of the mesa structure on which the n-side electrode 52 isformed. When the striped ridge structure is provided close to the n-sideelectrode 52 as in this example, the electric resistance and thus theoperating voltage is reduced.

Then, the p-side electrode 51 of nickel and gold is formed on thesurface of the SiO₂ insulation film 53 and the p-GaN p-type contactlayer 50. The n-side electrode 52 of titanium and aluminum is formed onthe surface of the n-GaN n-type contact layer 43 which has been exposedby the etching process. Thus, a gallium nitride type LD wafer isproduced.

Then, the wafer is cleaved along a direction perpendicular to thedirection of the ridge stripe so as to provide laser cavity end faces.Thereafter, each of the cleaved wafer pieces is further divided intoindividual chips. Each chip is mounted on a stem, and the electrodes arerespectively connected to lead terminals by wire bonding, therebyproducing a gallium nitride type semiconductor laser device.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 15 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation. When the gallium nitride typesemiconductor laser device of this example is used in an optical disksystem, a data read error is prevented. Thus, there is provided agallium nitride type semiconductor laser device which can be put intopractical use.

In the present example, the width of the current injection stripe regionis about 1.0 μm. However, substantially the same effect can be achievedwith any other width of the stripe region in a range between about 0.2μm and about 1.8 μm.

In the present example, each of the quantum well layers and the barrierlayers of the multiquantum well structure active layer 46 has athickness of about 5 nm. However, these layers need not have the samethickness but may alternatively have different thicknesses. Moreover,substantially the same effect can be achieved as long as each of theselayers has a thickness of about 10 nm or less. Furthermore, themultiquantum well structure active layer 46 may alternatively includetwo or four quantum well layers, or it may alternatively be a singlequantum well layer structure active layer.

In the present example, the laser cavity end faces are provided bycleavage. However, a sapphire substrate may sometimes be so hard that itis difficult to be cleaved. In such a case, the laser cavity end facesmay alternatively be provided by a dry etching process.

Moreover, since a sapphire substrate, which is an insulator, is used inthe present example, the n-side electrode 52 is formed on the surface ofthe n-GaN n-type contact layer 43 which has been exposed by the etchingprocess. Alternatively, when GaN, SiC, Si, GaAs, or the like, having then-type conductivity, is used for the substrate, the n-side electrode 52may be formed on the reverse side of the substrate. In such a case, theetching process for producing a striped mesa structure having a width ofabout 200 μm may be optional, and the striped ridge structure into whicha current is injected may be separated by about 3 μm or more from eachend of the semiconductor laser device chip.

Moreover, the p-type and n-type conductivities may be reversed in theabove explanation.

EXAMPLE 6

FIG. 4 is a cross-sectional view illustrating a gallium nitride typesemiconductor laser device according to Example 6 of the presentinvention.

Referring to FIG. 4, the gallium nitride type semiconductor laser deviceincludes an insulative GaN substrate 61 having a c-plane as a topsurface thereof, an n-GaN n-type contact layer 62, ann-Al_(0.1)Ga_(0.9)N n-type cladding layer 63, an n-GaN guide layer 64, amultiquantum well structure active layer 65 including threeIn_(0.2)Ga_(0.8)N quantum well layers and four In_(0.05)Ga_(0.95)Nbarrier layers, a p-GaN guide layer 66, a p-Al_(0.1)Ga_(0.9)N p-typefirst cladding layer 67, a p-Al_(0.1)Ga_(0.9)N p-type second claddinglayer 68, a p-GaN p-type contact layer 69, a p-side electrode 70, ann-side electrode 71 and a Si-doped n-Al_(0.25)Ga_(0.75)N currentblocking layer 72.

In the present example, the Si-doped n-Al_(0.25)Ga_(0.75)N layer is usedas a current blocking layer. Alternatively, any other semiconductor maybe used as long as it has a refractive index less than or equal to thatof the Mg-doped p-Al_(0.1)Ga_(0.1)N p-type cladding layer. For example,an AlGaN ternary mixed crystal nitride semiconductor having a differentAl composition, an AlGaInN quaternary mixed crystal nitridesemiconductor, or a semiconductor other than a nitride semiconductor maybe used. However, when a gallium nitride type semiconductor is used fora current blocking layer, the thermal expansion coefficient, the latticeconstant and the crystalline structure thereof are similar to those ofthe other gallium nitride type semiconductors used for the active layeror the cladding layer. Thus, a current blocking layer having a goodcrystallinity can be formed, thereby improving the reliability of thelaser device.

The GaN substrate used in the present example has a lattice constantwhich is close to that of a gallium nitride type semiconductor materialdeposited thereon, thereby resulting in a film with good crystallinity.Furthermore, it is relatively easily cleaved, thereby facilitatingformation of a laser cavity end face by cleavage. However, the substratewhich can be used in the present invention is not limited to a GaNsubstrate. For example, a sapphire substrate, a SiC substrate, a spinelsubstrate, a MgO substrate, a Si substrate, a GaAs substrate, or thelike, may be used instead of a GaN substrate. When a sapphire substrateis used, in order to reduce the lattice constant difference between thenitride semiconductor and the sapphire substrate, a gallium nitride typesemiconductor buffer layer may be provided on the sapphire substratebefore depositing the multilayer structure of the semiconductor laserdevice.

Each of the n-type cladding layer 63 and the p-type cladding layers 67and 68 may alternatively be made of an AlGaN ternary mixed crystalhaving an Al composition other than Al_(0.1)Ga_(0.9)N. When the Alcomposition is increased, the energy gap difference and the refractiveindex difference between the active layer and the cladding layerincreases, thereby effectively confining carriers and light within theactive layer. This allows for reduction of the oscillation thresholdcurrent and improvement of the temperature characteristic. Decreasingthe Al composition to such an extent that the confinement of carriersand light is maintained increases the mobility of the carriers in thecladding layers, thereby allowing for reduction of the device resistanceof the semiconductor laser device. Moreover, each of these claddinglayers may alternatively be made of a quaternary mixed crystalsemiconductor, or a mixed crystal semiconductor of more than fourelements which further contains one or more additional elements in asmall amount. The n-type cladding layer 63 and the p-type claddinglayers 67 and 68 need not have the same mixed crystal composition.

Referring to FIG. 4, a method for producing the above-described galliumnitride type semiconductor laser device will now be described. In thefollowing, an MOCVD method is employed. However, any other vapor phasegrowth method with which GaN can be epitaxially grown may alternativelybe used, e.g., an MBE method or an HVPE method.

First, the Si-doped n-GaN n-type contact layer 62 is grown to be about 3μm in thickness at a growth temperature of about 1050° C., using TMG,NH₃ and SiH₄ as source materials, on the insulative GaN substrate 61having a c-plane as a top surface thereof which has been positioned in apreselected growth oven. Then, TMA is added to the source materials, andthe Si-doped Al_(0.1)Ga_(0.9)N n-type cladding layer 63 is grown to beabout 0.7 μm while maintaining the growth temperature at about 1050° C.Then, the Si-doped n-GaN guide layer 64 is grown to be about 0.05 μmwhile maintaining the growth temperature at about 1050° C.

Next, the growth temperature is reduced to about 750° C., and anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm), anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm), anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm) and anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm) are grown inthis order, using TMG, NH₃ and TMI as source materials, therebyproviding the multiquantum well structure active layer 65 (totalthickness: about 35 nm).

Next, the growth temperature is increased again to about 1050° C., andthe Mg-doped p-GaN guide layer 66 is grown to be about 0.05 μm inthickness, using TMG, NH₃ and Cp₂Mg as source materials. Then, TMA isadded to the source materials, and the p-Al_(0.1)Ga_(0.9)N p-type firstcladding layer 67 is grown to be about 0.2 μm while maintaining thegrowth temperature at about 1050° C. Then, the Si-dopedn-Al_(0.25)Ga_(0.75)N current blocking layer 72 is grown to be about 0.3pm while maintaining the growth temperature at about 1050° C., usingTMG, NH₃, TMA and SiH₄ as source materials.

After the above-described crystal growth steps, the resulting wafer istaken out of the growth oven and, using ordinary photolithography anddry etching techniques, a dry etching process is performed to remove aportion of the n-Al_(0.25)Ga_(0.75)N current blocking layer 72 so as toprovide a striped groove having a width of about 1.0 μm which reachesthe p-Al_(0.1)Ga_(0.9)N p-type first cladding layer 67. The dry etchingis stopped before reaching the multiquantum well structure active layer65 so as to suppress damage to the active layer due to the etching,thereby preventing the reliability of the device from decreasing and theoscillation threshold current value from increasing.

Then, the wafer is again positioned in the growth oven, and the Mg-dopedp-Al_(0.1)Ga_(0.9)N p-type second cladding layer 68 is grown in thestripe grooves each having a width of about 1.0 μm and substantiallyover the entire surface of the n-Al_(0.25)Ga_(0.75)N current blockinglayer 72 with a growth temperature of about 1050° C., using TMG, TMA,NH₃ and Cp₂Mg as source materials. The Mg-doped p-Al_(0.1)Ga_(0.9)Np-type second cladding layer 68 is formed to be about 0.5 μm inthickness. Then, TMA is removed from the source materials, and theMg-doped p-GaN p-type contact layer 69 is grown to be about 0.2 μm inthickness while maintaining the growth temperature at about 1050° C.Thus, a gallium nitride type epitaxial wafer is produced.

Then, the wafer is annealed in a nitrogen gas atmosphere at about 800°C., so as to reduce the resistance of the Mg-doped p-type layers.

Thereafter, using ordinary photolithography and dry etching techniques,an etching process is performed to remove portions of the p-GaN p-typecontact layer 69 and the other layers thereunder where the stripedgroove having a width of about 1.0 μm are not provided so that the n-GaNn-type contact layer 62 is exposed. Thus, a striped mesa structure areprovided to have a width of about 200 μm and include the groove having awidth of about 1.0 μm. The striped groove having a width of about. 1.0μm is preferably separated by about 3 μm or more from each side of themesa structure having a width of about 200 μm. In the present example,the striped groove is provided so as to be separated by about 5 μm froma side of the mesa structure on which the n-side electrode 71 is formed.

Then, the p-side electrode 70 of nickel and gold is formed on thesurface of the p-GaN p-type contact layer 69, which is at the top of themesa structure having a width of about 200 μm. The n-side electrode 71of titanium and aluminum is formed on the surface of the n-GaN n-typecontact layer 62 which has been exposed by the etching process. Thus, agallium nitride type LD wafer is produced.

Then, the wafer is cleaved along a direction perpendicular to thedirection of the groove stripe so as to provide laser cavity end faces,and each of the cleaved wafer pieces is further divided into individualchips. Each chip is mounted on a stem, and the electrodes arerespectively connected to lead terminals by wire bonding, therebyproducing a gallium nitride type semiconductor laser device.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 15 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation. When the gallium nitride typesemiconductor laser device of this example is used in an optical disksystem, a data read error is prevented. Thus, there is provided agallium nitride type semiconductor laser device which can be put intopractical use.

In the present example, the width of each of the striped grooves intowhich a current is injected is about 1.0 μm. However, substantially thesame effect can be achieved with any other width of the stripe region ina range between about 0.2 μm and about 1.8 μm.

In the present example, each of the quantum well layers and the barrierlayers of the multiquantum well structure active layer 65 has athickness of about 5 nm. However, these layers need not have the samethickness but may alternatively have different thicknesses. Moreover,substantially the same effect can be achieved as long as each of theselayers has a thickness of about 10 nm or less. Furthermore, themultiquantum well structure active layer 65 may alternatively includetwo or four quantum well layers, or it may alternatively be a singlequantum well layer structure active layer.

In the present example, the laser cavity end faces are provided bycleavage. The laser cavity end faces may alternatively be provided by adry etching process.

Moreover, since an insulative substrate is used in the present example,the n-side electrode 71 is formed on the surface of the n-GaN n-typecontact layer 62 which has been exposed by the etching process.Alternatively, when GaN, SiC, Si, GaAs, or the like, having the n-typeconductivity, is used for the substrate, the n-side electrode 71 may beformed on the reverse side of the substrate. In such a case, the etchingprocess for producing a striped mesa structure having a width of about200 μm may be optional, and the striped groove into which a current isinjected may be separated by about 3 μm or more from each end of thesemiconductor laser device chip.

Moreover, the p-type and n-type conductivities may be reversed in theabove explanation.

In the present example, the p-Al_(0.1)Ga_(0.9)N p-type first claddinglayer 67 and the p-Al_(0.1)Ga_(0.9)N p-type second cladding layer 68have the same composition. Therefore, the lateral mode lasercharacteristic of the device is not affected by the remaining thicknessof the etched portion of the p-Al_(0.1)Ga_(0.9)N p-type first claddinglayer 67 which has been etched during the dry etching process foretching a portion of the n-Al_(0.25)Ga_(0.75)N current blocking layer 72to form the striped grooves. This is because the same gallium nitridetype semiconductor composition is employed for the p-type cladding layerwhich is provided in the striped groove. Thus, good lasercharacteristics can be obtained even when there is variation in thethickness of the unetched portion of the p-Al_(0.1)Ga_(0.9)N p-typefirst cladding layer 67.

Moreover, when it is possible, by controlling the etching rate, toprecisely control the remaining thickness of the etched portion of thep-Al_(0.1)Ga_(0.9)N p-type first cladding layer 67, thep-Al_(0.1)Ga_(0.9)N p-type first cladding layer 67 and thep-Al_(0.1)Ga_(0.9)N p-type second cladding layer 68 need not to have thesame composition to obtain good laser characteristics withoutvariations.

EXAMPLE 7

FIG. 5 is a cross-sectional view illustrating a gallium nitride typesemiconductor laser device according to Example 7 of the presentinvention.

Referring to FIG. 5, the gallium nitride type semiconductor laser deviceincludes an insulative GaN substrate 81 having a c-plane as a topsurface thereof, an n-GaN n-type contact layer 82, ann-Al_(0.1)Ga_(0.9)N n-type cladding layer 83, an n-GaN guide layer 84, amultiquantum well structure active layer 85 including twoIn_(0.2)Ga_(0.8)N quantum well layers and three In_(0.05)Ga_(0.95)Nbarrier layers, a p-GaN guide layer 86, a p-Al_(0.1)Ga_(0.9)N p-typeetching stopping layer 87, a p-Al_(0.1)Ga_(0.9)N p-type cladding layer88, a p-GaN p-type contact layer 89, a p-side electrode 90, an n-sideelectrode 91 and a Si-doped n-In_(0.25)Ga_(0.75)N current blocking layer92.

In the present example, the Si-doped n-In_(0.25)Ga_(0.75)N layer is usedas a current blocking layer. Alternatively, any other semiconductor maybe used as long as it has an energy gap less than or equal to that ofthe active layer. For example, an InGaN ternary mixed crystal nitridesemiconductor having a different In composition, an AlGaInN quaternarymixed crystal nitride semiconductor, or a semiconductor other than anitride semiconductor such as a gallium arsenide type semiconductor, anindium phosphide type semiconductor, a II-VI group semiconductor, a IVgroup semiconductor, or the like, may be used. However, when a galliumnitride type semiconductor is used for a current blocking layer, thethermal expansion coefficient, the lattice constant and the crystallinestructure thereof are similar to those of the other gallium nitride typesemiconductors used for the active layer or the cladding layer.Therefore, a current blocking layer having a good crystallinity can beformed, thereby improving the reliability of the laser device.

Referring to FIG. 5, a method for producing the above-described galliumnitride type semiconductor laser device will now be described. In thefollowing, an MOCVD method is employed. However, any other vapor phasegrowth method with which GaN can be epitaxially grown may alternativelybe used, e.g., an MBE method or an HVPE method.

First, the Si-doped n-GaN n-type contact layer 82 is grown to be about 3μm in thickness at a growth temperature of about 1050° C., using TMG,NH₃ and SiH₄ as source materials, on the insulative GaN substrate 81having a c-plane as a top surface thereof which has been positioned in apreselected growth oven. Then, TMA is added to the source materials, andthe Si-doped n-Al_(0.1)Ga_(0.9)N n-type cladding layer 83 is grown to beabout 0.7 μm in thickness while maintaining the growth temperature atabout 1050° C. Then, TMA is removed from the source materials, and theSi-doped p-GaN guide layer 84 is grown to be about 0.05 μm in thicknesswhile maintaining the growth temperature at about 1050° C.

Next, the growth temperature is reduced to about 750° C., and anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm), anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm) and anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm) are grown inthis order, using TMG, NH₃ and TMI as source materials, therebyproviding the multiquantum well structure active layer 85 (totalthickness: about 25 nm).

Next, the growth temperature is increased again to about 1050° C., andthe Mg-doped p-GaN guide layer 86 is grown to be about 0.05 μm inthickness, using TMG, NH₃ and Cp₂Mg as source materials. Then, TMA isadded to the source materials, and the Mg-doped p-Al_(0.1)Ga_(0.9)Np-type etching stopping layer 87 is grown to be about 0.05 μm whilemaintaining the growth temperature at about 1050° C. Then, the growthtemperature is reduced to about 750° C., and the Si-dopedn-In_(0.25)Ga_(0.75)N current blocking layer 92 is grown to be about 0.3μm, using TMG, NH₃, TMI and SiH₄ as source materials.

After the above-described crystal growth steps, the resulting wafer istaken out of the growth oven and, using ordinary photolithography anddry etching techniques, a dry etching process is performed to remove aportion of the n-In_(0.25)Ga_(0.75)N current blocking layer 92 so as toprovide a striped groove having a width of about 1.0 μm which reachesthe p-Al_(0.1)Ga_(0.9)N p-type etching stopping layer 87. In thisprocess, Al atoms appear on the exposed surface when the etching reachesthe p-Al_(0.05)Ga_(0.95)N etching stopping layer 87. Thus, the etchingprocess can be stopped upon detection of the Al atoms by elementanalysis, thereby precisely controlling the etching depth.

Then, the wafer is again positioned in the growth oven, and the Mg-dopedp-Al_(0.1)Ga_(0.9)N p-type cladding layer 88 is grown in the stripegroove having a width of about 1.0 μm and substantially over the entiresurface of the n-In₂₅Ga_(0.75)N current blocking layer 92 with a growthtemperature of about 1050° C., using TMG, TMA, NH₃ and Cp₂Mg as sourcematerials. The Mg-doped p-Al_(0.1)Ga_(0.9)N p-type cladding layer 88 isformed to be about 0.7 μm in thickness. Then, TMA is removed from thesource materials, and the Mg-doped p-GaN p-type contact layer 89 isgrown to be about 0.2 μm in thickness while maintaining the growthtemperature at about 1050° C. Thus, a gallium nitride type epitaxialwafer is produced.

Then, the wafer is annealed in a nitrogen gas atmosphere at about 800°C., so as to reduce the resistance of the. Mg-doped p-type layers.

Thereafter, using ordinary photolithography and dry etching techniques,an etching process is performed to remove portions of the p-GaN p-typecontact layer 89 and the other layers thereunder where the stripedgroove having a width of about 1.0 μm are not provided so that the n-GaNn-type contact layer 82 is exposed. Thus, a striped mesa structures areprovided to have a width of about 200 μm and include the groove having awidth of about 1.0 μm. The striped groove having a width of about 1.0 μmis preferably separated by about 3 μm or more from each side of the mesastructure having a width of about 200 μm. In the present example, thestriped groove is provided so as to be separated by about 5 μm from aside of the mesa structure on which the n-side electrode 91 is formed.

Then, the p-side electrode 90 of nickel and gold is formed on thesurface of the p-GaN p-type contact layer 89, which is at the top of themesa structure having a width of about 200 μm. The n-side electrode 91of titanium and aluminum is formed on the surface of the n-GaN n-typecontact layer 82 which has been exposed by the etching process. Thus, agallium nitride type LD wafer is produced.

Then, the wafer is cleaved along a direction perpendicular to thedirection of the groove stripe so as to provide laser cavity end facesand each of the cleaved wafer pieces is further divided into individualchips. Each chip is mounted on a stem, and the electrodes arerespectively connected to lead terminals by wire bonding, therebyproducing a gallium nitride type semiconductor laser device.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 18 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation. When the gallium nitride typesemiconductor laser device of this example is used in an optical disksystem, a data read error is prevented. Thus, there is provided agallium nitride type semiconductor laser device which can be put intopractical use.

In the present example, the width of each of the striped grooves intowhich a current is injected is about 1.0 μm. However, substantially thesame effect can be achieved with any other width of the stripe region ina range between about 0.2 m and about 1.8 μm.

In the present example, the p-Al_(0.1)Ga_(0.9)N p-type etching stoppinglayer 87 and the p-Al_(0.1)Ga_(0.9)N p-type cladding layer 88 have thesame composition. Alternatively, these layers may have differentcompositions, respectively. Moreover, the Al composition of thep-Al_(0.1)Ga_(0.9)N p-type etching stopping layer 87 is not limited tothat illustrated in this example. Any other semiconductor may be used aslong as it allows for determination of the etching depth. When the Alcomposition is less than that of the p-type cladding layer 88 andgreater than that of the p-GaN guide layer 86, the energy gap of thep-type etching stopping layer 87 is between that of the p-type claddinglayer 88 and that of the p-GaN guide layer 86. This causes an energygradient for injecting holes from the p-type cladding layer 88 into thep-GaN guide layer 86, thereby facilitating the injection.

In the present example, the p-Al_(0.1)Ga_(0.9)N p-type etching stoppinglayer 87 is deposited on the p-GaN guide layer 86. Alternatively, thep-Al_(0.1)Ga_(0.9)N p-type etching stopping layer 87 may be deposited inthe p-GaN guide layer 86.

EXAMPLE 8

FIG. 6 is a cross-sectional view illustrating a gallium nitride typesemiconductor laser device according to Example 8 of the presentinvention.

Referring to FIG. 6, the gallium nitride type semiconductor laser deviceincludes a sapphire substrate 101 having a c-plane as a top surfacethereof, a GaN buffer layer 102, an n-GaN n-type contact layer 103, ann-Al_(0.1)Ga_(0.8)N n-type cladding layer 104, an n-GaN guide layer 105,a multiquantum well structure active layer 106 including twoIn_(0.2)Ga_(0.8)N quantum well layers and a single In_(0.05)Ga_(0.95)Nbarrier layer, an Al_(0.2)Ga_(0.8)N evaporation prevention layer 107, ap-GaN guide layer 108, a p-Al_(0.1)Ga_(0.9)N p-type cladding layer 109,a p-GaN p-type contact layer 110, a p-side electrode 111, an n-sideelectrode 112 and a SiO₂ insulation film 113.

Referring to FIG. 6, a method for producing the above-described galliumnitride type semiconductor laser device will now be described. In thefollowing, an MOCVD method is employed. However, any other vapor phasegrowth method with which GaN can be epitaxially grown may alternativelybe used, e.g., an MBE method or an HVPE method.

First, the GaN buffer layer 102 is grown to be about 35 nm in thicknessat a growth temperature of about 550° C., using TMG and NH₃ as sourcematerials, on the sapphire substrate 101 having a c-plane as a topsurface thereof which has been positioned in a preselected growth oven.

Then, the growth temperature is increased to about 1050° C., and theSi-doped n-GaN n-type contact layer 103 is grown to be about 3 μm inthickness, using TMG, NH₃ and SiH₄ as source materials.

After the above-described crystal growth steps, the resulting wafer istaken out of the growth oven, and the SiO₂ insulation film 113 having athickness of about 200 nm is formed as a current blocking layer on thesurface of the Si-doped n-GaN n-type contact layer 103. Moreover, usingordinary photolithography and wet etching techniques, the SiO₂insulation film 113 is wet-etched with fluorine so as to form a stripedgroove having a width of about 1.0 μm.

Then, the wafer is again positioned in the growth oven, and the Si-dopedn-Al_(0.1)Ga_(0.9)N n-type cladding layer 104 is grown to be about 0.7μm in thickness while maintaining the growth temperature at about 1050°C., using TMG, TMA, NH₃ and SiH₄ as source materials. Then, TMA isremoved from the source materials, and the Si-doped n-GaN guide layer105 is grown to be about 0.05 μm in thickness while maintaining thegrowth temperature at about 1050° C.

Next, the growth temperature is reduced to about 750° C., and anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm), anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm) and anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm) are grownin this order, using TMG, NH₃ and TMI as source materials, therebyproviding the multiquantum well structure active layer 106 (totalthickness: about 15 nm). Then, the Al_(0.2)Ga_(0.8)N evaporationprevention layer 107 is grown to be about 10 nm in thickness, using TMG,TMA and NH₃ as source materials, while maintaining the growthtemperature at about 750° C. Next, the growth temperature is increasedagain to about 1050° C., and the Mg-doped p-GaN guide layer 108 is grownto be about 0.05 μm in thickness, using TMG, NH₃ and Cp₂Mg as sourcematerials. Then, TMA is added to the source materials, and the Mg-dopedp-Al_(0.1)Ga_(0.9)N p-type cladding layer 109 is grown to be about 0.7μm in thickness while maintaining the growth temperature at about 1050°C. Then, TMA is removed from the source materials, and the Mg-dopedp-GaN p-type contact layer 110 is grown to be about 0.2 μm in thicknesswhile maintaining the growth temperature at about 1050° C. Thus, agallium nitride type epitaxial wafer is produced. In the above process,the n-Al_(0.1)Ga_(0.9)N n-type cladding layer 104, the n-GaN guide layer105, the multiquantum well structure active layer 106, theAl_(0.2)Ga_(0.8)N evaporation prevention layer 107, the p-GaN guidelayer 108, the p-Al_(0.1)Ga_(0.9)N p-type cladding layer 109 and p-GaNp-type contact layer 110 are each formed in a ridge structure centeredalong the striped groove having a width of about 1.0 μm.

Then, the wafer is annealed in a nitrogen gas atmosphere at about 800°C., so as to reduce the resistance of the Mg-doped p-type layers.

Thereafter, using ordinary photolithography and wet etching techniques,an etching process is performed to remove portions of the SiO₂insulation film 113 on which the ridge structure is not formed in astriped pattern having a width of about 100 μm until the n-GaN n-typecontact layer 103 is exposed.

Then, the p-side electrode 111 of nickel and gold is formed on thesurface of the p-GaN p-type contact layer 110. The n-side electrode 112of titanium and aluminum is formed on the surface of the n-GaN n-typecontact layer 103 which has been exposed by the etching process. Thus, agallium nitride type LD wafer is produced.

Then, the wafer is cleaved along a direction perpendicular to thedirection of the ridge stripe so as to provide laser cavity end faces,and each of the cleaved wafer pieces is further divided into individualchips. Each chip is mounted on a stem, and the electrodes arerespectively connected to lead terminals by wire bonding, therebyproducing a gallium nitride type semiconductor laser device.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 18 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation. When the gallium nitride typesemiconductor laser device of this example is used in an optical disksystem, a data read error is prevented. Thus, there is provided agallium nitride type semiconductor laser device which can be put intopractical use.

In the present example, the width of the current injection stripe regionis about 1.0 μm. However, substantially the same effect can be achievedwith any other width of the stripe region in a range between about 0.2μm and about 1.8 μm.

Moreover, in the present example, a gallium nitride type semiconductorlayer having the n-type conductivity is provided on the sapphiresubstrate 101, and then a gallium nitride type semiconductor layerhaving the p-type conductivity is provided thereon. Alternatively, thep-type and n-type conductivities may be reversed. In such a case, theAl_(0.1)Ga_(0.9)N cladding layer which is deposited after forming thecurrent blocking layer has the p-type conductivity, and thus, theelectric resistance is increased. Therefore, the current constricted bythe current blocking layer is prevented from spreading in thep-Al_(0.1)Ga_(0.9)N p-type cladding layer, thereby reducing theoscillation threshold current value.

EXAMPLE 9

FIG. 7 is a cross-sectional view illustrating a gallium nitride typesemiconductor laser device according to Example 9 of the presentinvention.

Referring to FIG. 7, the gallium nitride type semiconductor laser deviceincludes a sapphire substrate 121 having a c-plane as a top surfacethereof, a GaN buffer layer 122, an p-GaN p-type contact layer 123, ap-In_(0.05)Ga_(0.95)N etching stopping layer 124, a p-Al_(0.1)Ga_(0.9)Np-type cladding layer 125, an p-GaN guide layer 126, a multiquantum wellstructure active layer 127 including two In_(0.2)Ga_(0.8)N quantum welllayers and three In_(0.05)Ga_(0.95)N barrier layers, a n-GaN guide layer128, an n-Al_(0.1)Ga_(0.9)N n-type cladding layer 129, a n-GaN n-typecontact layer 130, a p-side electrode 131, an n-side electrode 132 and aSi-doped n-Al_(0.25)Ga_(0.75)N current blocking layer 133.

In the present example, the Si-doped n-Al_(0.25)Ga_(0.75)N layer is usedas a current blocking layer. Alternatively, any other semiconductor maybe used as long as it has a refractive index less than or equal to thatof the Mg-doped p-Al_(0.1)Ga_(0.9)N p-type cladding layer. For example,an AlGaN ternary mixed crystal nitride semiconductor having a differentAl composition, an AlGaInN quaternary mixed crystal nitridesemiconductor, or a semiconductor other than a nitride semiconductor maybe used. However, when a gallium nitride type semiconductor is used fora current blocking layer, the thermal expansion coefficient, the latticeconstant and the crystalline structure thereof are similar to those ofthe other gallium nitride type semiconductors used for the active layeror the cladding layer. Therefore, a current blocking layer having a goodcrystallinity can be formed, thereby improving the reliability of thelaser device.

Referring to FIG. 7, a method for producing the above-described galliumnitride type semiconductor laser device will now be described. In thefollowing, an MOCVD method is employed. However, any other vapor phasegrowth method with which GaN can be epitaxially grown may alternativelybe used, e.g., an MBE method or an HVPE method.

First, the GaN buffer layer 122 is grown to be about 35 nm in thicknessat a growth temperature of about 550° C., using TMG and NH₃ as sourcematerials, on the sapphire substrate 121 having a c-plane as a surfacethereof which has been positioned in a preselected growth oven.

Then, the growth temperature is increased to about 1050° C., and theMg-doped p-GaN p-type contact layer 123 is grown to be about 3 μm inthickness, using TMG, NH₃ and Cp₂Mg as source materials. Then, thegrowth temperature is reduced to about 750° C., TMI is added to thesource materials, and the Mg-doped p-In_(0.05)Ga_(0.95)N etchingstopping layer 124 is grown to be about 0.02 μm in thickness. Then, thegrowth temperature is increased again to about 1050° C., and theSi-doped n-Al_(0.25)Ga_(0.75)N current blocking layer 133 is grown to beabout 0.2 μm in thickness, using TMG, TMA, NH₃ and SiH₄ as sourcematerials.

After the above-described crystal growth steps, the resulting wafer istaken out of the growth oven and, using ordinary photolithography anddry etching techniques, a dry etching process is performed to remove aportion of the Si-doped n-Al_(0.25)Ga_(0.75)N current blocking layer 133so as to provide a striped groove having a width of about 1.0 μm. Inthis process, In atoms appear on the exposed surface when the etchingreaches the p-In_(0.05)Ga_(0.95)N etching stopping layer 124. Therefore,the etching process can be stopped upon detection of the In atoms byelement analysis, thereby precisely controlling the etching depth.

Then, the wafer is again positioned in the growth oven, and the Mg-dopedp-Al_(0.1)Ga_(0.9)N p-type cladding layer 125 is grown to be about 0.7μm in thickness at a growth temperature of about 1050° C., using TMG,TMA, NH₃ and Cp₂Mg as source materials. Then, TMA is removed from thesource materials, and the Mg-doped p-GaN guide layer 126 is grown to beabout 0.05 μm in thickness while maintaining the growth temperature atabout 1050° C.

Next, the growth temperature is reduced to about 750° C., and anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm), anIn_(0.05)Ga _(0.95)N barrier layer (thickness: about 5 nm), anIn_(0.2)Ga_(0.8)N quantum well layer (thickness: about 5 nm) and anIn_(0.05)Ga_(0.95)N barrier layer (thickness: about 5 nm) are grown inthis order, using TMG, NH₃ and TMI as source materials, therebyproviding the multiquantum well structure active layer 127 (totalthickness: about 25 nm). Next, the growth temperature is increased againto about 1050° C., and the Si-doped n-GaN guide layer 128 is grown to beabout 0.05 μm in thickness, using TMG, NH₃ and SiH₄ as source materials.Then, TMA is added to the source materials, and the Si-dopedn-Al_(0.1)Ga_(0.9)N n-type cladding layer 129 is grown to be about 0.7pm in thickness while maintaining the growth temperature at about 1050°C. Then, TMA is removed from the source materials, and the Si-dopedn-GaN n-type contact layer 130 is grown to be about 0.2 μm in thicknesswhile maintaining the growth temperature at about 1050° C. Thus, agallium nitride type epitaxial wafer is produced.

Then, the wafer is annealed in a nitrogen gas atmosphere at about 800°C., so as to reduce the resistance of the Mg-doped p-type layers.

Thereafter, using ordinary photolithography and dry etching techniques,an etching process is performed to remove portions of the n-GaN n-typecontact layer 130 on which the striped groove having a width of about1.0 μm are not formed until the p-GaN p-type contact layer 123 isexposed. Thus, a striped mesa structure is provided to have a width ofabout 200 μm and include the groove having a width of about 1.0 μm. Thestriped groove having a width of about 1.0 μm is preferably separated byabout 3 μm or more from each side of the mesa structure having a widthof about 200 μm. In the present example, the striped groove is providedso as to be separated by about 5 μm from a side of the mesa structure onwhich the p-side electrode 131 is formed.

Then, the n-side electrode 132 of titanium and aluminum is formed on thesurface of the n-GaN n-type contact layer 130 which is at the top of themesa structure having a width of about 200 μm. The p-side electrode 131of nickel and gold is formed on the surface of the p-GaN p-type contactlayer 123 which has been exposed by the etching process. Thus, a galliumnitride type LD wafer is produced.

Then, the wafer is cleaved along a direction perpendicular to thedirection of the ridge stripe so as to provide laser cavity end faces,and each of the cleaved wafer pieces is further divided into individualchips. Each chip is mounted on a stem, and the electrodes arerespectively connected to lead terminals by wire bonding, therebyproducing a gallium nitride type semiconductor laser device.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 15 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation. When the gallium nitride typesemiconductor laser device of this example is used in an optical disksystem, a data read error is prevented. Thus, there is provided agallium nitride type semiconductor laser device which can be put intopractical use.

In the present example, the width of the current injection stripe regionis about 1.0 μm. However, substantially the same effect can be achievedwith any other width of the stripe region in a range between about 0.2μm and about 1.8 μm.

In the present example, the p-In_(0.05)Ga_(0.95)N etching stopping layer124 is provided between the p-GaN p-type contact layer 123 and thep-Al_(0.1)Ga_(0.9)N p-type cladding layer 125. Alternatively, thep-In_(0.05)Ga_(0.95)N etching stopping layer 124 may be provided in thep-Al_(0.1)Ga_(0.9)N p-type cladding layer 125.

Moreover, in the present example, a gallium nitride type semiconductorlayer having the p-type conductivity is provided on the sapphiresubstrate 121, and then a gallium nitride type semiconductor layerhaving the n-type conductivity is provided thereon. Alternatively, thep-type and n-type conductivities may be reversed. In such a case, theactive layer is formed on a gallium nitride type semiconductor havingthe n-type conductivity which is generally of a better quality than agallium nitride type semiconductor having the p-type conductivity, thusimproving the reliability of the device.

EXAMPLE 10

A gallium nitride type semiconductor laser device according to Example10 of the present invention is produced in substantially the same manneras that in Example 9, except that a Mg-doped p-Al_(0.1)Ga_(0.9)N layeris used as an etching stopping layer and a Si-dopedn-In_(0.25)Ga_(0.75)N layer having a thickness of about 0.2 μm is usedas a current blocking layer. A portion of the Si-dopedn-In_(0.25)Ga_(0.75)N current blocking layer is etched so as to providea striped groove having a width of about 1.0 μm. In this process, Alatoms appear on the exposed surface when etching reaches thep-Al_(0.1)Ga_(0.9)N etching stopping layer. Therefore, the etchingprocess can be stopped upon detection of the Al atoms by elementanalysis, thereby precisely controlling the etching depth.

The produced semiconductor laser device exhibits good lasercharacteristics, e.g., an oscillation wavelength of about 410 nm and anoscillation threshold current of about 18 mA. Moreover, deterioration isnot observed in these characteristics, and it is confirmed that thedevice effects self-pulsation. In the present example, light generatedby the active layer is absorbed by the Si-doped n-In_(0.25)Ga_(0.75)Ncurrent blocking layer provided outside the current injection striperegion. The spreading of the lateral mode of the laser light isstabilized due to this light absorption by the current blocking layer,thereby allowing laser light of a single lateral mode to be obtainedwith good reproducibility.

In the present example, the Si-doped n-In_(0.25)Ga_(0.75)N layer is usedas a current blocking layer. Alternatively, any other semiconductor maybe used as long as it has an energy gap less than or equal to that ofthe active layer. For example, an InGaN ternary mixed crystal nitridesemiconductor having a different In composition, an AlGaInN quaternarymixed crystal nitride semiconductor, or a semiconductor other than anitride semiconductor such as a gallium arsenide type semiconductor, anindium phosphide type semiconductor, a II-VI group semiconductor, a IVgroup semiconductor, or the like, may be used. However, when a galliumnitride type semiconductor is used for a current blocking layer, thethermal expansion coefficient, the lattice constant and the crystallinestructure thereof are similar to those of the other gallium nitride typesemiconductors used for the active layer or the cladding layer.Therefore, a current blocking layer having a good crystallinity can beformed, thereby improving the reliability of the laser device.

As described above, in the gallium nitride type semiconductor laserdevice of the present invention, a current is injected into a striperegion having a width smaller than that of the active layer. The widthof the current injection stripe region is preferably in a range betweenabout 0.2 μm and about 1.8 μm. As a result, a portion of the activelayer existing in the area outside the stripe region where the laserlight is spreading can absorb the laser light. Thus, the portion of theactive layer outside the current injection stripe region functions as asaturable absorbing layer, thereby obtaining the self-pulsationcharacteristic.

Even when the width of the stripe region is small as in the presentinvention, there is little current spreading since a gallium nitridetype semiconductor material has a large electric resistance value. Thus,a gallium nitride type semiconductor laser device with a low oscillationthreshold current value and good laser oscillation characteristics canbe obtained.

Moreover, when the width of the stripe region is reduced as in thepresent invention, the number of defects within the region is reduced,thereby preventing deterioration of the laser characteristics andimproving the reliability of the device.

Thus, the present invention realizes a gallium nitride typesemiconductor laser device with satisfactory laser oscillationcharacteristics which can be used for an optical disk and which does notcause an error during a data read operation.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A gallium nitride type semiconductor laserdevice, comprising: a substrate; and a layered structure formed on thesubstrate, the layered structure at least including an active layer of anitride type semiconductor material which is interposed between a pairof nitride type semiconductor layers each functioning as a claddinglayer or a guide layer, wherein a current is injected into a striperegion in the layered structure having a width smaller than a width ofthe active layer, and the width of the stripe region is in a rangebetween about 0.2 μm and about 1.8 μm.
 2. A gallium nitride typesemiconductor laser device according to claim 1, wherein a portion ofthe active layer existing outside the stripe region has a width of atleast about 3 μm.
 3. A gallium nitride type semiconductor laser deviceaccording to claim 1, wherein the active layer comprises a singlequantum well layer.
 4. A gallium nitride type semiconductor laser deviceaccording to claim 3, wherein a thickness of the single quantum welllayer in the active layer is about 10 nm or less.
 5. A gallium nitridetype semiconductor laser device according to claim 1, wherein the activelayer comprises a multiquantum well structure including a plurality ofquantum well layers and at least one barrier layer each interposedbetween the adjacent two quantum well layers, the number of the quantumwell layers being two, three or four.
 6. A gallium nitride typesemiconductor laser device according to claim 5, wherein a thickness ofeach of the quantum well layers in the active layer is about 10 nm orless.
 7. A gallium nitride type semiconductor laser device according toclaim 5, wherein a thickness of each of the at least one barrier layerin the active layer is about 10 nm or less.
 8. A gallium nitride typesemiconductor laser device according to claim 1, wherein: the layeredstructure at least includes a first cladding layer having a firstconductivity type, the active layer, a second cladding layer having asecond conductivity type, and a contact layer having the secondconductivity type, which are deposited in this order; the secondcladding layer and the contact layer are formed in a stripe having awidth smaller than the width of the active layer; and the layeredstructure further includes a current blocking layer deposited outsidethe stripe.
 9. A gallium nitride type semiconductor laser deviceaccording to claim 8, wherein the current blocking layer comprises adielectric insulation film.
 10. A gallium nitride type semiconductorlaser device according to claim 8, wherein the current blocking layer ismade of a semiconductor material having an energy gap which is equal toor smaller than an energy gap of the active layer.
 11. A gallium nitridetype semiconductor laser device according to claim 10, wherein thecurrent blocking layer is made of a nitride type semiconductor material.12. A gallium nitride type semiconductor laser device according to claim8, wherein the current blocking layer is made of a semiconductormaterial having a refractive index which is less than or equal to arefractive index of the cladding layer having the second conductivity.13. A gallium nitride type semiconductor laser device according to claim12, wherein the current blocking layer is made of a nitride typesemiconductor material.
 14. A gallium nitride type semiconductor laserdevice according to claim 8, wherein a thickness of a gallium nitridetype semiconductor layer included in the layered structure andinterposed between a portion of the active layer outside the striperegion and the current blocking layer is in a range between about 0.01μm and about 0.8 μm.
 15. A gallium nitride type semiconductor laserdevice according to claim 1, wherein: the layered structure at leastincludes a first cladding layer having a first conductivity type, theactive layer, a guide layer or a second cladding layer having a secondconductivity type, and a current blocking layer; a striped groove isprovided in the current blocking layer so as to reach the guide layer orthe second cladding layer having the second conductivity type, thegroove having a width smaller than the width of the active layer; andthe layered structure further includes at least another cladding layerhaving the second conductivity type and a contact layer having thesecond conductivity type which are deposited in this order in thestriped groove and on the current blocking layer.
 16. A gallium nitridetype semiconductor laser device according to claim 15, wherein thecurrent blocking layer comprises a dielectric insulation film.
 17. Agallium nitride type semiconductor laser device according to claim 15,wherein the current blocking layer is made of a semiconductor materialhaving an energy gap which is equal to or smaller than an energy gap ofthe active layer.
 18. A gallium nitride type semiconductor laser deviceaccording to claim 17, wherein the current blocking layer is made of anitride type semiconductor material.
 19. A gallium nitride typesemiconductor laser device according to claim 15, wherein the currentblocking layer is made of a semiconductor material having a refractiveindex which is less than or equal to a refractive index of the claddinglayer having the second conductivity.
 20. A gallium nitride typesemiconductor laser device according to claim 19, wherein the currentblocking layer is made of a nitride type semiconductor material.
 21. Agallium nitride type semiconductor laser device according to claim 15,wherein a thickness of a gallium nitride type semiconductor layerincluded in the layered structure and interposed between a portion ofthe active layer outside the stripe region and the current blockinglayer is in a range between about 0.01 μm and about 0.8 μm.
 22. Agallium nitride type semiconductor laser device according to claim 1,wherein: the layered structure at least includes a contact layer or acladding layer having a first conductivity type, and a current blockinglayer, which are deposited in this order; a stripe groove is provided inthe current blocking layer so as to reach the contact layer or thecladding layer having the first conductivity type; and the layeredstructure further includes at least another cladding layer having thefirst conductivity type, the active layer, a cladding layer having asecond conductivity type, and a contact layer having the secondconductivity type, which are deposited in this order in the stripedgroove and on the current blocking layer.
 23. A gallium nitride typesemiconductor laser device according to claim 22, wherein the currentblocking layer comprises a dielectric insulation film.
 24. A galliumnitride type semiconductor laser device according to claim 22, whereinthe current blocking layer is made of a semiconductor material having anenergy gap which is equal to or smaller than an energy gap of the activelayer.
 25. A gallium nitride type semiconductor laser device accordingto claim 24, wherein the current blocking layer is made of a nitridetype semiconductor material.
 26. A gallium nitride type semiconductorlaser device according to claim 22, wherein the current blocking layeris made of a semiconductor material having a refractive index which isless than or equal to a refractive index of the cladding layer havingthe second conductivity.
 27. A gallium nitride type semiconductor laserdevice according to claim 26, wherein the current blocking layer is madeof a nitride type semiconductor material.
 28. A gallium nitride typesemiconductor laser device according to claim 22, wherein a thickness ofa gallium nitride type semiconductor layer included in the layeredstructure and interposed between a portion of the active layer outsidethe stripe region and the current blocking layer is in a range betweenabout 0.01 μm and about 0.8 μm.
 29. A gallium nitride type semiconductorlaser device according to claim 1 wherein the semiconductor laser devicehas a low oscillation threshold current value.
 30. A gallium nitridetype semiconductor laser device according to claim 29 wherein thesemiconductor laser device sustains a self-pulsating state.
 31. Agallium nitride type semiconductor laser device according to claim 1wherein the semiconductor laser device includes a multi-quantum wellstructure having quantum well layers and barrier layers arranged in analternating pattern.
 32. A gallium nitride type semiconductor laserdevice according to claim 1 including a quantum well layer, the quantumwell layer having a thickness of about 10 nm or less.
 33. A galliumnitride type semiconductor laser device according to claim 1 wherein thesemiconductor laser device sustains a self-pulsating state.